This invention relates generally to ink compositions, and more particularly to heterogeneous low energy gel ink compositions. Even more particularly, the present invention relates to ink compositions that contain a colorant, a latex, a polyol and/or a diol, a dispersant such as a sulfonated polyester, and a liquid vehicle such as water.
In general, phase change inks (sometimes referred to as “hot melt inks” and/or “gel inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device, such as a piezoelectric ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify or become immobilized to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Gel inks can be considered a particular type of phase change inks. In gel inks, the ink compositions generally exist as stable, often liquid, compositions at low temperature, but form solutions of very high viscosity at high temperatures and/or when water is removed from the ink. The type of phase change that occurs is from the stable liquid to a higher viscosity gel matrix, which still contains liquid components. Thus, the gel inks can be used to print on a heated substrate, or can be used to print on a lower temperature substrate when a heating device is used, such as a radiant heater or a fuser.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. Nos. 4,889,560, 4,889,761, and 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks have also been used for applications such as postal marking, industrial marking, and labeling, as well as for both office and production printing applications including specialty applications.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. Nos. 3,653,932, 4,390,369, 4,484,948, 4,684,956, 4,851,045, 4,889,560, 5,006,170, 5,151,120, 5,372,852, and 5,496,879, European Patent Publications 0187352 and 0206286, German Patent Publications DE 4205636AL and DE 4205713AL, and PCT Patent Application WO 94/04619, the disclosures of each of which are totally incorporated herein by reference. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
While known compositions and processes are suitable for their intended purposes, a need remains for phase change and other inks that are suitable for ink jet printing processes, such as piezoelectric ink jet printing processes and the like. In addition, a need remains for inks that can be jetted at lower temperatures than currently known phase change inks, thereby enabling reduced energy use and improved thermal stability of the ink. Further, a need remains for inks that exhibit desirably low viscosity values at jetting temperatures, thereby enabling increased jetting frequency. Additionally, a need remains for inks that generate images having a desirably low coefficient of friction, thereby improving performance when substrates having the inks printed thereon are passed through automatic document handlers in copiers and also improving feel of the image and in some cases improving dry smear characteristics. There is also a need for inks that generate images with reduced pile height. In addition, there is a need for inks that generate images with improved scratch resistance. Further, there is a need for inks that generate images with improved look and feel characteristics. Additionally, there is a need for inks that generate images with improved permanence and toughness characteristics. A need also remains for inks that are suitable for high speed printing, thereby enabling transaction and production printing applications.
For example, despite these various ink designs, however, improved ink compositions are still required. In particular, improved ink compositions are required to provide improved print performance, such as permanence and robustness on a variety of print substrates, improved optical density, less showthrough (i.e., appearance from an opposite side of the printed substrate), and the like.